Used as a stable isotope-labeled internal standard in mass spectrometry and nuclear magnetic resonance (NMR) studies to accurately quantify aspartic acid and related metabolites in biological samples. Enables precise tracking of metabolic pathways, including the urea cycle and amino acid metabolism, in research involving protein turnover, neurological disorders, and cancer metabolism. Its isotopic enrichment allows differentiation from endogenous aspartic acid, improving measurement accuracy in complex matrices like plasma, urine, and tissue extracts. Also employed in stable isotope labeling by amino acids in cell culture (SILAC) for proteomic studies.